The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Hyperbaric chambers have been regularly used in many applications, including medical applications. For example, hyperbaric chambers have been used for hyperbaric oxygen therapy for treating many medical conditions and for training regimens such as the treatment of severe burns, peripheral vascular disease, carbon monoxide poisoning, decompression illness and the like. Pressure in hyperbaric chambers can be varied from atmospheric pressure to a desired level greater than atmospheric pressure.
Hyperbaric chambers generally include at least one entry into the chamber. These entries may or may not include an airlock. Known entries include a door swings into the chamber to open. Thus, when closed, the door is pressed against the inside of the frame of the chamber. In this configuration, the pressure inside the chamber facilitates the sealing of the door. In other words, since the pressure inside the chamber is greater than that outside the chamber, the door is further pressed against the inside of the frame of the chamber to secure the door in the closed position and make a pressure-tight seal.
In contrast to hyperbaric chambers, hypobaric pressure chambers allow a low-pressure or vacuum-like environment to be maintained within the chamber. Hypobaric chambers can be useful in many applications such as simulation of high-altitude environments which may be experienced by, for example, pilots or astronauts.
Hypobaric chambers typically include an entry door that swings outward so that the pressure differential causes the door to be pulled against the frame of the chamber. One such hypobaric chamber is illustrated in U.S. Pat. No. 5,503,143.
Although hypobaric chambers have a significant number of applications, the cost of building a hypobaric chamber to meet acceptable standards can be prohibitive. Rather, it would be preferable to provide a way to use a chamber designed for hyperbaric applications as a hypobaric chamber or a dual-use (hyperbaric/hypobaric) pressure chamber.